HLA-C and atrial fibrillation: Consistently, we found that oxidative stress (indicated by increased ROS generation, Figure 3), myofibril degradation (indicated by decreased MHC expression, Figure 4), and fibrosis (indicated by increased collagen generation, Figure 5) were more severe in the atria of AF patients homozygous for longer alleles than those homozygous for shorter alleles and SR control.